The invention relates to a process for the preparation of surface-modified inorganic fillers and pigments of a defined grain size, the thus obtained fillers and pigments, and the use thereof.
In many fields of technology, inorganic pigments or fillers are bound with binders in the form of polymer dispersions, for example, in the preparation of dispersion paints, adhesives or paper.
EP 0 515 928 B1 relates to surface-modified platelet-like pigments with improved repulping behavior, and a process for the preparation thereof, and the use thereof. Said platelet-like pigments, for example, platelet-like metals, metal oxides, mica pigments and other platelet-like substrates, are coated with a polyacrylate or polymethacrylate or their water-soluble salts and optionally a solvent or mixture of solvents in a mixing vessel with stirring.
For example, in the preparation of paper, a large amount of fillers is employed. Almost all papers are admixed with fillers, which provide a uniform formation, better softness, whiteness and grip to printing and writing papers, in particular.
Natural printing papers (uncoated papers) contain up to 35% by weight of fillers, coated papers contain from 25 to 50% by weight of fillers. The amount of fillers is highly dependent on the intended use of the paper. Heavily loaded papers have lower strengths and a poorer sizing capability.
The filler content in the paper composition is usually from 5 to 35% by weight and consists of primary pigments or recirculated coating pigments which may be derived from residual coats or coated rejects. In addition to the whiteness of the filler, which is important for fluorescent whitened paper, the grain size plays an important role, because it highly influences the filler yield and the physical properties of the paper, especially its porosity. The filler content remaining in the paper is from 20 to 80% by weight of the amount added to the fiber suspension. The yield depends on both the type of filler and the composition of matter, the degree of milling, the fixing of the filler particles by resin and aluminum sulfate, the basis weight, the speed of the paper machine, the way of water withdrawal, and the fineness of the screen.
As judged by their consumption, the following products have rather great importance today as fillers and coating pigments: china clay, calcium carbonate, artificial aluminum silicates and oxide hydrates, titanium dioxide, satin white, talcum and calcium silicate.
EP 0 595 723 B1 describes a process for the preparation of mineral-based loading pigments, characterized in that a co-milling of a compacting mineral, a lamellar mineral and/or a plastic pigment in performed in aqueous medium in the presence of at least one milling aid comprising at least one dispersing agent. However, this document remains too vague with respect to the conditions in the co-milling of mineral and plastic pigment and fails to mention the use of dispersing agents.
WO 98/01621 describes a process for the reuse of fillers and coating pigments from the preparation of paper, paperboard and cardboard from the residual water sludges from coating plant waste waters, drinking plants, internal water treatment plants or separators, and the use of a thus obtained pigment slurry for the preparation of a coating composition for the paper industry, or for use in the paper stock for papermaking. An essential element of the invention is a process for reusing fillers and coating pigments from the preparation of paper, paperboard and cardboard from the residual water sludges from coating plant waste waters, drinking plants, internal water treatment plants or separators which is characterized in that said residual water sludges containing fillers and coating pigments are subjected to mixing and subsequently milling to form a pigment slurry with fresh pigment or fresh filler as powders, slurry containing fresh pigment and/or slurry containing fresh filler.